Reduction of explosion hazards in the separation of gaseous mixtures



March 12, 1963 w, E. GORDON ETAL 3,080,724

REDUCTION OF EXPLOSION HAZARDS IN THE SEPARATION OF GASEOUS MIXTURES Filed Sept. 19, 1958 INVENTORS. W/LL/AM E GORDON W4 RRE/V A. SALMON ATTORNEYS Uite 3,080,724 Patented Mar. 12, 1963 REDUCTION OF EXPLOSION HAZARDS IN THE SEPARATION OF GASEOUS MIXTURES William E. Gordon, Winchester, and Warren A. almon, Lexington, Mass, assignors to Arthur D. Little, Inc.,

a corporation of Massachusetts Filed Sept. 19, 1958, Ser. No. 762,119 30 Claims. (Cl. 62-20) This invention broadly relates to improvement in the separation of gaseous mixtures into at least two fractions and, in one of its more specific aspects, to a novel method of reducing the explosion hazard associated with the separation of gaseous mixtures into a plurality of fractions in a fractionating operation.

The present invention is particularly useful in the environment of an atmospheric air fractionating operation of the prior art wherein a liquid oxygen-rich fraction containing high boiling impurities of a nature which will form an explosive mixture with liquid oxygen is collected in a collecting zone. While the invention will be described and illustrated hereinafter with specific reference to such an atmospheric air fractionating operation, it is expressly understood that the principles of the invention also are applicable to other low temperature fractionating operations of the prior art in which a gaseous mixture containing hazardous impurities is separated into two or more fractions.

As is well known, high boiling point impurities present in gaseous mixtures must be removed in order to prevent dilficulties in the operation of low temperature fractionating cycles. For example, in the separation of air into oxygen and nitrogen components, carbon dioxide, hydrocarbon contaminants, and other high boiling point impurities in the atmospheric air feed to the cycle would precipitate and collect in the cycle, thereby affecting operation of the cycle and eventually requiring suspension of operations for removal of the collected impurities. In order to obtain continuous operation, it is necessary to remove substantially the total high boiling point impurity content present in the feed to the cycle.

The high boiling point impurities which still get into the cycle may be removed by warming up or defrosting the plant and when only inert impurities such as carbon dioxide are present they do not constitute a hazard. However, when high boiling point impurities such as acetylene, lubricating oils, etc. are present, they concentrate in the colder portions of the cycle, such as in the liquid oxygen component contained in the refluxing condenser, and thereby tend to produce an explosive mixture. For example, as the cycle is continuously operated over an extended period of time, the concentration of high boiling point hydrocarbon impurity in the reboiler condenser gradually increases until eventually a point is reached where an explosive mixture of liquid oxygen-rich com ponent and hydrocarbon impurity is produced. In addition, upon warming up the cycle, the liquid oxygenrich fraction containing the hydrocarbon impurities is allowed to evaporate, thereby increasing the concentration of high boiling point hydrocarbon impurities and eventually producing an explosive concentration with the remaining liquid oxygen-rich fraction.

The presence of high boiling point hydrocarbon impurities in the feed to an air fractionating cycle and the tendency of such substances to concentrate in an oxygenrich fraction to thereby cause an explosion hazard has resulted in a long standing problem in the art. Much time and effort has been spent in attempting to solve the problem and prior to the present invention several expedients were known for reducing the extent of dangerous hydrocarbon concentration in an air separation plant. These previously known expedients include the use of silica gel beds to adsorb the hydrocarbons, extending the air intake outside areas contaminated with hydrocarbons, the use of a sacrificial element wherein the hydrocarbons collect and possibly explode without doing extensive damage to the remaining equipment, and periodic withdrawal of liquid oxygen component containing hydrocarbons from the refluxing condenser or sacrificial element in order to remove unwanted hydrocarbon condensates. These expcdients have not been entirely satisfactory. For example, atmospheric air almost always contains a small amount of hydrocarbon impurities which are very difficult to remove completely by adsorbents. Also adsorbers must be taken oifstream periodically and reactivated at the proper time. When the hydrocarbon level inthe feed to the adsorber increases unexpectedly, the capacity of the adsorber will be reached before reactivation is normally due and the absorber then will be ineffective to completely remove hydrocarbons from the feed, thereby allowing the same to enter the cycle. In addition, where liquid oxygen containing hydrocarbons is periodically withdrawn from the refluxing condenser or sacrifical element, it usually is not possible to know when withdrawal of the liquid oxygen contents is necessary in order to maintain a safe level of hydrocarbon impurities unless the contents are more or less continuously tested by a troublesome and involved procedure. As a result of the above mentioned and other limitations and disadvantages of the prior art, those skilled in the art have long sought a satisfactory method for reducing the explosion hazard associated with the low temperature fractionation of a gaseous mixture.

The present invention overcomes the limitations and disadvantages of the prior art and provides an entirely satisfactory method of reducing the explosion hazard associated with a low temperature fractionating operation for separating gaseous mixtures containing hazardous impurities into a plurality of fractions. In accordance with the present invention, the explosion hazard is reduced by dissolving an inert halogenated hydrocarbon desensitizer having at least one fluorine atom in a fraction containing the hazardous impurity.

It is an object of the present invention to provide a novel method of reducing the explosion hazard associated with a gaseous mixture fractionating operation.

It is a further object of the present invention to provide a novel method of reducing the explosion hazard ass sociated with an atmospheric air fractionating operation.

It is still a further object of the present invention to provide a novelv method of separating atmospheric air into oxygen-rich and nitrogen-rich fractions in a fractionating operation whereby the explosion hazard is reduced.

It is still a further object of the present invention to provide a novel method of warming up atmospheric air fractionating apparatus including a liquid oxygen-rich fraction collecting zone whereby the explosion hazard is reduced.

Still other objects and advantages of the present invention will be apparent to those skilled in the art by reference to the following detailed description and the drawing, which diagrammatically illustrates a representative atmospheric air fractionating cycle embodying the principles of the present invention.

Referring now to the drawing, atmospheric air under superatmospheric pressure is conducted by conduit 10 to scrubber 11 where carbon dioxide, hydrogen sulphide, and other objectionable acidic impurities are removed. Gaseous effluent is withdrawn from scrubber 11 and conducted via conduit 12 to drier 14 for the removal of moisture, and then gaseous eflluent substantially free. of acidic inn purities and moisture is withdrawn and conducted via conduit 15 to path 16 of heat exchange device 17 for passing in heat exchange relationship with the cold prodnet of a fractionating operation to be described in detail hereinafter. The gaseous eflluent flows through path 16 and emerges from the cold end of heat exchange device 17 in conduit 18 at a temperature slightly above the saturation temperature at the existing pressure, and it is then expanded in valve 19 to a relatively low superatmospheric pressure corresponding to the pressure existing within the high pressure section of the fractionating column to be described in detail hereinafter.

The conduit 20 conducts the stream of expanded atmospheric air from expansion valve 19 to the high pressure section 21 of a two-stage fractionating column 22. The fractionating column 22 may be of a conventional construction including high pressure section 21, low pressure section 23, refluxing condenser 24, and with fractionating trays 25 or other suitable liquid-vapor contacting means being provided in both the high pressure 21 and the low pressure section 23. The expanded atmospheric air feed undergoes preliminary separation in high pressure section 21 producing a liquid oxygen-rich fraction which collects in pool 26 in the base of fractionating column 22, and a gaseous nitrogen-rich fraction which flows upwardly into refluxing condenser 24 where it is liquefied in heat exchange effecting relationship with oxygen-rich liquid collecting in pool 27 in the base of the low pressure section 23 and surrounding tubes 28 of refluxing condenser 24. The liquefied nitrogen-rich fraction flows downwardly from refluxing condenser 24, with a portion being used in the high pressure section 21 as reflux and with another portion being collected in the pool 29 below refluxing condenser 24. A stream of liquefied nitrogen-rich fraction is withdrawn from pool 29 by conduit 30, expanded in valve 31, and then conducted via conduit 32 to the upper end of low pressure section 23 and introduced therein as reflux.

A stream of liquid oxygen-rich fraction is withdrawn from pool 26 by conduit 33 as feed for the low pressure section 23. The conduit 33 is connected through conduits 34 and 35 and switching valves 36 and 37 to adsorbers 38 and 39, respectively. The adsorbers 38 and 39, in turn, are connected through conduits 40 and 41 and switching valves 42 and 43, respectively, to conduit 44 including expansion valve 45. The adsorbers 38 and 39 may be of a conventional type suitable for the re moval of hydrocarbons or other undesirable high boiling point impurities and may be packed with silica gel or other effective adsorbent for such high boiling point impurities. The adsorbers 38 and 39 are provided in duplicate so that upon proper operation of the switching 'valves 36, 37, 42, and 43, one adsorber will be onstream while the other adsorber will be oflstream for reactivation. Reactivation is accomplished by flowing a stream of warm product gas or other warm clean fluid stream via conduit 46, conduit 47, conduit 34 or 35 dependent upon the position of control valves 48 and 49, and then through adsorber 38 or 49, respectively. It is then withdrawn from adsorber 38 or 39 via conduit 40 or 41, and conduit 50 including control valve 51 or conduit 52 including control valve 53, respectively. For example, when adsorber 38 is onstream and adsorber 39 is offstream, control valves 36, 42, 49 and 53 are open, control valves 37, 43, 48 and 51 are closed, and a warm fluid stream is passed to adsorber 39 via conduit 46, conduit 47 including open control valve 49, and conduit 35, and it is withdrawn from adsorber 39 via conduit 41 and conduit 52 including open control valve 53. If desired, the adsorbers 38 and 39 may be bypassed by closing valves 36, 37, 42 and 43, opening valve 54 in conduit 55, and passing the feed for low pressure section 23 directly from conduit 33 to conduit 44 via conduit 55.

The feed for low pressure section 23 is withdrawn via conduit 44, expanded in expansion valve 45, and then fed to the upper portion of low pressure section 23. Separation of the gaseous mixture is completed in the low pressure section 23 producing oxygen-rich liquid which collects in pool 27, and a nitrogen-rich fraction in gaseous phase which flows upwardly into the dome of fractionating column 22 and is withdrawn therefrom by way of conduit 56. The conduit 56 conducts a stream of gaseous nitrogen-rich component to the cold end of path 57 in heat exchange device 17 where it is warmed in countercurrent heat exchange effecting relation with the incoming stream of atmospheric air in path 16, and the warmed stream of gaseous nitrogen-rich component leaves the cycle by way of conduit 58 at substantially ambient temperature and atmospheric pressure. Depending upon whether gaseous or liquid oxygen-rich component is desired as a product, which in turn will depend upon the manner in which fractionating column 22 is operated, oxygen-rich component may be withdrawn in liquid phase by way of conduit 59 including control valve 60, or oxygen-rich component may be delivered in gaseous phase by way of conduit 61 including control valve 62. Conduit 61 communicates with path 63 in heat exchange device 17, in which the stream of gaseous oxygen-rich component flows in countercurrent heat exchange effecting relation with the incoming stream of atmospheric air in path 16. The warmed oxygen-rich component leaves the cycle by way of conduit 64 at substantially atmospheric pressure and ambient temperature.

An inert halogenated hydrocarbon desensitizer may be supplied to the low pressure section 23 of fractionating column 22 via conduits 65 and 66 upon closing control valve 67 and opening control valve 68 or, if desired, the densensitizer may be supplied to high pressure section 21 via conduits 65 and 66 upon closing control valve 68 and opening control valve 67.

It will be understood that the specific type and form of gaseous mixture fractionating systems do not enter into the present invention except insofar as they present a body or bodies of liquefied gas containing impurities which form an explosive mixture, which body or bodies during continuous operation, or during warm-up, of the systems tend to increase in impurity concentration.

The desensitizers useful in practicing the present invention are inert halogenated hydrocarbons containing at least one fluorine atom which are soluble in effective amount in the substance to be desensitized. Preferably, the halogenated hydrocarbons are saturated but, in instances where they are sufiiciently inert, unsaturated halogenated hydrocarbons may be used.

The preferred halogenated hydrocarbons contain at least one fluorine atom and from one to five, inclusive, carbon atoms which may be in the form of a straight or branched chain. Specific examples of preferred inert halogenated hydrocarbons which have been found to be very satisfactory in practicing the present invention include CHF CI, CF CI CF Br., CF Cl and C 1 Often, CF Cl and CF Br give the best results due to, in part, their greater solubility in liquid oxygen. The halogenated hydrocarbons may be used separately or as mixtures and, in some instances, mixtures may be used to give physical characteristics which are more suitable for the type of protection desired in a specific application. The above halogenated hydrocarbons are often readily available in commercial quantities and, in addition, suitable processes for their preparation are well known.

The preferred halogenated hydrocarbons possess a unique combination of chemical and physical properties which result in their suitability for the desensitization of a liquid oxygen-rich fraction containing high boiling point impurities of a nature that form an explosive mixture with liquid oxygen. These unique chemical and physical prop erties include an extended liquid range, a very low vapor pressure at liquid oxygen temperature, solibility in liquid oxygen and an ability to desensitize liquid oxygen as distinguished from acting as a mere diluent. More specifically, the preferred halogenated hydrocarbons preferably have the following characteristics:

1) Appreciable solubility in liquid oxygen or other substance to be desensitized in a range of at least a few mol percent;

(2) A boiling point relatively high compared with the boiling point of oxygen or other liquefied gas which is being desensitized;

(3) A vapor pressure in the vapor space above the solution of halogenated hydrocarbon and liquid oxygen or other substance to be desensitized no greater than about one micron; and

(4) The halogenated hydrocarbon should be relatively inert, e.g., it should not be readily oxidizable or exhibit an appreciable tendency toward formation of an explosive mixture in the presence of liquid oxygen at liquid oxygen temperatures and when operating in accordance with the present invention.

In several embodiments of the present invention, a most desirable and unique property of the preferred halogenated hydrocarbons is a very low vapor pressure at liquid oxygen temperatures, such as a vapor pressure of the order of 10- to mm. Hg. Thus, in instances where a liquid oxygen-rich fraction is being evaporated, such as in the refluxing condenser of an air fractionating cycle producing gaseous oxygen product, the halogenated hydrocarbon remains behind in solution in the oxygenrich fraction and there is virtually no contamination of the gaseous oxygen product with halogenated hydrocarbon. In addition, during warm-up the halogenated hydrocarbon concentrates in the liquid oxygen-rich fraction along with high boiling point impurities in precisely those areas where the impurities concentrate. This results in a relatively small amount of halogenated hydrocarbon being eiiective as a desenitizer upon warm-up even when added to a relatively large body of liquid oxygen-rich fraction which contains a small or trace amount of high boiling point impurities.

A liquid oxygen-rich fraction may be either completely desensitized or only partially desensitized, depending upon the amount of inert halogenated hydrocarbon added and, to some extent, the amount or nature of the high boiling point impurity or impurities which are present. In view of this, it is not practical to set definite upper and lower limits for the amount of halogenated hydrocarbon to be dissolved in the liquid oxygen-rich fraction other than to state it should be dissolved in quantities effective to produce the desired degree of protection at a given concentration of a specific high boiling point impurity or impurities. In general, however, the halogenated hydrocarbon should be present in an amount of about 05-50 mol percent. ln the specification and claims, the mol percent of halogenated hydrocarbon is based upon the total molar quantity of liquid oxygen and halogenated hydrocarbon in the body of liquid being desensitized unless otherwise indicated. Thus, a mixture containing one mol of oxygen in a liquid oxygen-rich fraction, one mol of halo-genated hydrocarbon, and high boiling point impurities would be considered as containing 50 mol percent of halogenated hydrocarbon for the purpose of the present invention.

The halogenated hydrocarbon need be dissolved in the liquid oxygen-rich fraction in only relatively small quantities for complete protection against the more insoluble and most dangerous contaminants such as acetylene and lubricating oil. Generally, a quantity as small as 10-25 mol percent will give complete protection when liquid oxygen is saturated with these contaminants. Where smaller amounts of acetylene and lubricating oil are present, or where it is not necessary to provide complete pro tection, then smaller amounts may be used. Other hy drocarbon contaminants such as methane, ethane and ethylene present a less serious explosion hazard than does acetylene and lubricating oil. These substances are more soluble in liquid oxygen, as well as more volatile, and a much higher concentration must be present before an explosive concentration is reached. For example, methane must be present in liquid oxygenv to the extent of at least about 10 mol percent before an explosion can occur, while only very small quanities such as a few parts per million of acetylene and lubricating oil will result in the formation of sol-id particles which are very sensitive to explosive initiation. The greater volatility of these more soluble high boiling point impurities requires that they be present in the input air to the air fractionating cycle in relatively large concentrations and over a relatively long period of time in order to produce an explosive concentration. For example, methane must be present in the feed to the air fractionating cycle in an amount of at least about one mol percent in order to produce an explosive concentration. Thus, the tendency of methane and other lower hydrocarbons to concentrate and produce an explosive mixture in the refluxing condenser of an air fractionating cycle is not as great as that of high boiling point impurities such as acetylene and lubricating oil. This is of importance since liquid oxygen containing 33 mol percent methane, i.e., a stoichiometric solution of methane and liquid oxygen, requires about 50 mol percent of halogenated hydrocarbon to completely suppress an explosion. However, with smaller amounts of methane such as about 18 mol percent, about 20 mol percent of halogenated hydrocarbon will completely suppress an explosion. In instances where only trace or very small amounts of high boiling point impurities are present, even smaller amounts of the halogenated hydrocarbon are required.

It will be apparent from the foregoing that, when only the more common and most dangerous contaminants are present, usually about l025 mol percent and preferably, about 20 mol percent of the inert halogenated hydrocarbon desensitizer need be dissolved. in the liquid oxygenrich fraction for complete protection against explosion. When only partial protection against explosion is neces sary during operation of the air fractionating cycle, then a smaller amount of dissolved halogenated hydrocarbon is required. In instances where protection against explosion is necessary only during warm-up periods, then about 0.5-5 mol percent and, preferably, about 1-2 mol of the halogenated hydrocarbon need be added in most instances since it concentrates in the liquid oxygen-rich fraction along with the impurities and thus offers increased protection as the need for protection increases.

The minimum quantities of inert halogenated hydrocarbon required to completely suppress an explosion in various hydrocarbon-liquid oxygen mixtures are tabulated below. To illustrate that the halogenated hydrocarbons used in practicing the invention are not merely diluents, comparable figures are also given for nitrogen and argon.

It is apparent from the above tabulated data that only 20 mol percent of halogenated hydrocarbon is required to completely suppress an explosion when liquid oxygen is saturated with motor oil or acetylene, these substances being two of the most objectionable high boiling point contaminants. In contrast to this, it requires 60 to mol percent of nitrogen, or 70 mol percent of argon to dilute liquid oxygen saturated with motor oil and acetylene to a point where it is no longer explosive. Halogenated hydrocarbons such as GHF Cl, CF Cl CF Br, CFgCI and C F were tested in obtaining the above data, and were found to be substantially equally effective Ona mol percent basis.

The addition of a halogenated hydrocarbon desensitizer such as herein disclosed to a liquid oxygen-rich fraction is not the equivalent of addition of a diluent such as nitrogen or argon which, because of its inertncss, would render the liquid oxygen-rich fraction less reactive or act to take up energy and prevent an explosion from propagating. Rather, the effect of the halogenated hydrocarbon appears to be specific to a reaction between liquid oxygen and high boiling point impurity. For example, the halogenated hydrocarbons do not appear to act as diluents that merely take up heat since experimental data indicate that the heat capacity of a given halogenated hydrocarbon bears no relationship to the effectiveness of the compound as an inhibitor or desensitizer of explosion. Thus, halogenated hydrocarbons having heat capacity values covering a wide range are all substantially equally effective at a given mol percent concentration. While we do not wish to be bound by any explanation or theory, one plausible explanation for this unusual and unexpected result is that the halogenated hydrocarbon may actually enter into what may be considered to be a reaction with the liquid oxygen and high boiling point impurity under conditions which would ordinarily result in an explosion, and acts as a deterrent to the accompanying chain reaction. Qualitative experimental evidence indictaes that halogenated hydrocarbons act as chain stoppers in such chain reactions since if a powerful ignition system is applied to liquid oxygen containing high boiling point impurities and about 15 mol percent of the halogenated hydrocarbon, then localized reactions or explosions will take place but they are almost immediately halted.

The atmospheric air fractionating cycle illustrated in the drawing and described herein, or other suitable prior art fractionating cycle modified to provide means for introducing the inert halogenated hydrocarbon desensitizer at a desirable point in the cycle, generally may be operated substantially in accordance with conventional practice to separate atmospheric air, for example, into gaseous and/or liquid components such as gaseous oxygen and gaseous nitrogen components, or liquid oxygen and gaseous nitrogen components. At the most, generally it is only necessary to adjust conventional operating conditions to compensate for the slight rise in the boiling point of the oxygen-rich fraction due to the presence of dissolved inert halogenated hydrocarbon. For example, when the oxygen-rich fraction contains about 20 mol percent of dissolved halogenated hydrocarbon, the boiling point will rise about 1 C. and the normal operating pressure of the high pressure section, i.e., the pressure when operating without the dissolved halogenated hydrocarbon, should be increased about 510% for best results. However, this increase in the operating pressure of the high pressure section may be at least partially offset by increasing the size of the refluxing condenser in order to increase the efliciency of separation.

In operation of the cycle illustrated in the drawing for separating atmospheric air into gaseous oxygen and gaseous nitrogen components in accordance with one embodiment of the invention, atmospheric air under a pressure of about 200 p.s.i.a. enters the cycle through conduit and after removal of carbon dioxide and other objectional acidic impurities in scrubber 11 and drying in drier 14, it is passed in countercurrent heat exchange eflfecting relation with cold gaseous oxygen and nitrogen product in heat exchanger 17. The stream of air emerging from path 16 and flowing in conduit 18 is at a temperature only slightly above the saturation temperatureat the existing pressure, and it is expanded in valve 19 to about 85 p.s.i.a. with a concomitant drop in temperature below the saturation temperature at the exising pressure and passed into high pressure section 21. Partial liquefaction takes place in high pressure section 21 and the air feed undergoes preliminary separation producing a liquid oxygen-rich fraction which collects in pool 26 and a gaseous nitrogen-rich fraction which flows upwardly into refluxing condenser 24 where it is liquefied. The liquefied nitrogen-rich fraction flows downwardly from refluxing condenser 24, with a portion being used in the high pressure section as reflux, and with another portion being withdrawn from pool 29 by conduit 30, expanded in valve 31, and introduced into the low pressure section 23 as reflux. A stream of liquid oxygen-rich fraction is withdrawn from pool 26 via conduit 33 and fed to adsorber 38 via conduit 34 and open valve 36 where, in normal operation, hydrocarbons or other high boiling point impurities which will form an explosive mixture with liquid oxygen are removed by the silica gel adsorbent. However, the liquid oxygen-rich fraction which is withdrawn from adsorber 38 via conduits 40 and 41, expanded in valve 45 to about 20 p.s.i.a. and fed to low pressure section 23, may contain trace amounts of high boiling point impurities due to any one or more of a number of reasons such as failure to switch the adsorbers when the capacity of the onstream adsorber was reached, improper reactivation, mechanical failure, etc. In such event, the high boiling point impurities concentrate in the pool of liquid oxygen 27 and eventually reach explosive proportions. In accordance with one embodiment of the invention, the explosion hazard may be reduced by dissolving in the pool of liquid oxygen 27 a suitable quantity such as about 20 mol percent of inert halogenated hydrocarbon desensitizer, based on the total molar amount of liquid oxygen and halogenated hydrocarbon present in pool 27. The halogenated hydrocarbon may be fed to the low pressure section 23 in the proper amount via conduits 65 and 66 including open valve 68, and allowed to remain in the pool of liquid oxygen 27 permanently during operation of the cycle. There is no tendency toward contamination of the gaseous oxygen product with the halogenated hydrocarbon due to its extremely low vapor pressure at the boiling point of liquid oxygen. Separation of the gaseous mixture is completed in low pressure section 23 producing a gaseous nitrogen component which flows upwardly into the dome of tractionating column 22 and which is withdrawn therefrom via conduit 56. Gaseous oxygen component is withdrawn via conduit 61, and both the gaseous nitrogen and oxygen components are passed through heat exchanger 17 in heat exchange eflecting relation with the incoming air stream.

In another embodiment of the present invention, the air separation cycle may be operated as described above but without providing inert halogenated hydrocarbon desensitizer for the liquid oxygen in pool 27 until warmup of the apparatus. For example, a small amount of the halogenated hydrocarbon such as about 0.5-5 mol percent, based upon the total molar amount of liquid oxygen and halogenated hydrocarbon present, may be supplied to the liquid oxygen-rich fractions collecting in the low pressure section 23 and/ or the high pressure section 21 via conduits 65 and 66. This relatively small amount of desensitizer will concentrate during warmup along with the high boiling point impurities which are present in these fractions, and thus increases in effectiveness as the need for protection increases. It also is possible in accordance with the present invention to provide a liquid oxygen component which is desensitized with the halogenated hydrocarbon described herein. Such a desensitized liquid oxygen product may be subsequently handled without creating an explosion hazard and thus finds many uses in the art. When preparing a desensitized liquid oxygen product, the above cycle may be operated substantially in accordance with prior art practice to produce a liquid oxygen product, with the exception of feeding the desired amount of halogenated hydrocarbon to produce desensitized liquid oxygen, such as 0.5-5 mol percent based on the total molar amount of liquid oxygen and halogenated hydrocarbon present,

to either the low or high pressure sections 23 and 21 via conduits 65 and 66. When the halogenated hydrocarbon is fed to high pressure section 2.1, then. usually it is preferred to by-pass adsorbers 38 and 39 via conduit 55. The halogenated hydrocarbon collects in the pool of liquid oxygen 27, regardless of the feed point, and desensitized liquid oxygen. containing dissolved halogenated hydrocarbon is withdrawn from pool 27 via conduit 59 and open valve 60.

Although several embodiments of the present invention have been disclosed and described herein, it is understood that various changes and substitutions may be made therein without departing from the spirit of the invention, as will be well understood 'by those skilled in the art. For example, although the invention ha been described in the environment of an air separation cycle, it is to be expressly understood that the invention may be employed in the environment of fractionating cycles or operations designed for separating other gaseous mixtures.

What is claimed is:

1. In a fractionating operation wherein a normally gaseous mixture containing elemental oxygen and impurities comprising hydrocarbon contaminants which will form an explosive mixture with elemental oxygen is separated into at least two fractions, one of the separated fractions containing elemental oxygen and impurities comprising hydrocarbon contaminant-s which will form an explosive mixture with elemental oxygen and being collected in the liquid state in a body of liquid from which vapors are evolved during the fractionating operation, the method of reducing the explosion hazard comprising the step of adding to the body of liquid a soluble inert halogenated hydrocarbon having not less than one fluorine atom and not more than five carbon atoms.

2. The method of claim 1 hydrocarbon is CHFgCl.

3. The method of claim 1 hydrocarbon is CF Cl 4. The method of claim 1 hydrocarbon is CF Br.

5. The method of claim 1 hydrocarbon is CFgCl.

6. The method of claim 1 hydrocarbon is C 1 7. In an atmospheric air fractionating operation wherein an oxygen-rich fraction containing high boiling point impurities comprising hydrocarbon contaminants which will form an explosive mixture with liquid oxygen is collected in the liquid state in a body of liquid from which vapors are evolved during the fractionating op eration, the method of reducing the explosion hazard comprising the step of dissolving in the body of liquid a soluble inert halogenated hydrocarbon having not less than one fluorine atom and not more than five carbon atoms.

8. The method of claim 7 wherein the halogenated hydrocarbon is CHF CI.

9. The method of claim 7 wherein the halogenated hydrocarbon is CF CI 10. The method of claim 7 wherein the halogenated hydrocarbon is CF Br.

11. The method of claim 7 wherein the halogenated hydrocarbon is CF Cl.

12. The method of claim 7 wherein the halogenated hydrocarbon is C 1 13. In a method of warming up atmospheric air fractionating apparatus including a liquid oxygen-rich fraction collecting zone, in which method at least a portion of a body of liquid oxygen-rich fraction containing high boiling point impurities comprising hydrocarbon contaminants that will form an explosive mixture with liquid oxygen is removed from the collecting zone by vaporization, the improvement comprising the step of reducing wherein the halogenated wherein the halogenated wherein the halogenated wherein the halogenated wherein the halogenated 10 the explosion hazard by adding to the body a soluble inert halogenated hydrocarbon having not less than one fluorine atom and not more than five carbon atoms.

14. The method of claim 13 wherein the halogenated hydrocarbon is CHF CI.

15. The method of claim 13 wherein the halogenated hydrocarbon is CF Cl 16. The method of claim- 13 wherein the halogenated hydrocarbon is CF Br.

17. The method of claim 13 wherein the halogenated hydrocarbon is CF Cl.

18. The method of claim 13 wherein the halogenated hydrocarbon is C F 19. In a fractionating operation wherein a normally gaseous mixture containing elemental oxygen and impurities comprising hydrocarbon contaminants which will form an explosive mixture with elemental oxygen is separated into at least two fractions, one of the separated fractions containing elemental oxygen and impurities comprising hydrocarbon contaminants which will form an explosive mixture with elemental oxygen and being collected in the liquid state in a body of liquid from which vapors are evolved during the fractionating operation, the method of reducing the explosion hazard comprising the step of dissolving in the body of liquid a soluble inert halogenated hydrocarbon having not less than one fluorine atom and not more than five carbon atoms, the halogenated hydrocarbon being of the formula C X H wherein X is halogen and n and m are Whole numbers.

20. The method of claim 19 wherein n is less than 4.

21. The method of claim 19' wherein n is 1.

22. The method of claim 19 wherein n is 1 and m is equal to 2n+2.

23. In an atmospheric air fractionating operation wherein an oxygen-rich fraction containing high boiling point impurities comprising hydrocarbon contaminants which will form an explosive mixture with liquid oxygen is collected in the liquid state in a body of liquid from which vapors are evolved during the fractionating operation, the method of reducing the explosion hazard comprising the step of adding to the body of liquid a soluble inert halogenated hydrocarbon having not less than one fluorine atom and not more than five carbon atoms, the halogenated hydrocarbon being of the formula C X H wherein X is halogen and n and m are whole numbers.

24. The method of claim 23 wherein n is less than 4.

25. The method of claim 23 wherein n is 1.

26. The method of claim 23 wherein n is 1 and m is equal to 2n+2.

27. In a method of Warming up atmospheric air fractionating apparatus including a liquid oxygen-rich fraction collecting zone, in which method at least a portion of a body of liquid oxygen-rich fraction containing high boiling point impurities comprising hydrocarbon contaminants that will form an explosive mixture with liquid oxygen is removed from the collecting zone by vaporization, the improvement comprising the step of reducing the explosion hazard by adding to the body a soluble inert halogenated hydrocarbon having not less than one fluorine atom and not more than five carbon atoms, the halogenated hydrocarbon being of the formula C X H wherein X is halogen and n and m are whole numbers.

28. The method of claim 27 wherein n is less than 4.

29. The method of claim 27 wherein n is one.

30. The method of claim 27 wherein n is one and m is equal to 2n+2.

References Cited in the file of this patent UNITED STATES PATENTS 1,759,155 Farrington May 20, 1930 1,804,432 Pollitzer May 12, 1931 1,821,170 Linde Sept. 1, 1931 (fither references on following page) UNITED STATES PATENTS 3,008,902 COOk NOV. 14, 1961 E g FOREIGN PATENTS 2215102 Nilsi iiiiiiiiiiiiiiiii 501 9 1955 129,010 Great Britain 27, 1955 2:75:33 Johnson 1 955 5 1,246,273 France Oct 60 2,874,164 Hann Feb. 17, 1959 OTH REFERENCES 2,876,077 Haller Mar. 3, 1959 2,925,385 Winnacker Feb 16, 1960; Hamm: hemwal Engmeenng Progress, volume 51, 2 92 529 Grosse Man 15, 9 N m er 11, pages 523-527, November 1955.

2,992,540 Grosse July 18, 1961 

1. IN A FRACTIONATING OPERATION WHEREIN A NORMALLY GASEOUS MIXTURE CONTAINING ELEMENTAL OXYGEN AND IMPURITIES COMPRISING HYDROCARBON CONTAMINANTS WHICH WILL FORM AN EXPLOSIVE MIXTURE WITH ELEMENTAL OXYGEN IS SEPARATED INTO AT LEAST TWO FRACTIONS, ONE OF THE SEPARATED FRACTIONS CONTAINING ELEMENTAL OXYGEN AND IMPURITIES COMPRISING HYDROCARBON CONTAMINANTS WHICH WILL FORM AN EXPLOSIVE MIXTURE WITH ELEMENTAL OXYGEN AND BEING COLLECTED IN THE LIQUID STATE IN A BODY OF LIQUID FROM WHICH VAPORS ARE EVOLVED DURING THE FRACTIONATING OPERATION, THE METHOD OF REDUCING THE EXPLOSION HAZARD COMPRISING THE STEP OF ADDING TO THE BODY OF LIQUID A SOLUBLE INERT HALOGENATED HYDROCARBON HAVING NOT LESS THAN ONE FLUORINE ATOM AND NOT MORE THAN FIVE CARBON ATOMS. 